1. Field of the Invention
The present invention relates to a magnetic recording medium having a nonmagnetic base and a magnetic layer formed thereon containing magnetizable particles dispersed in a resinous binder.
2. Description of the Prior Art
In general, a magnetic recording medium is manufactured by the manner that a magnetic paint or composition containing predominantly magnetizable particles (magnetic powder), resinous binder and solvent is coated on a nonmagnetic base, for example, a base film and then dried to form a magnetic layer. In this case, a good dispersion of the magnetizable particles in the magnetic paint or composition is desirable, for such good dispersion brings about high S/N ratio, high squareness ratio which is a ratio of the residual flux density Br to the saturation flux density Bm, and high packing of the magnetizable particles. For improvement of the dispersion, there are some well-known methods in which, for example, a dispersion agent is added to the magnetic paint or composition, or the surface of the magnetizable particle is modified into an oleophilic surface. Dispersion agents conventionally used are fatty acids having carbon atoms of 12 to 18, estus of such fatty acid with alcohol, metallic salts, amides, sulfates and phosphates of such fatty acid. Lecithin, higher alcohols, higher amines and so on also well-known as such dispersion agents. On the other hand, for the modification treatment of magnetizable particle into oleophilic surfaces, an alkylation, alkoxysilane treatment, alkylchromate treatment and so on of hydroxyl groups in the surface of the magnetizable particle are well-known. However, the above-mentioned conventional dispersion agents and modification treatments are not satisfactory.